A lithographic apparatus is a machine that applies a desired pattern onto a substrate, usually onto a target portion of the substrate. A lithographic apparatus can be used, for example, in the manufacture of integrated circuits (ICs). In that instance, a patterning device, which is alternatively referred to as a mask or a reticle, may be used to generate a circuit pattern to be formed on an individual layer of the IC. This pattern can be transferred onto a target portion (e.g. comprising part of, one, or several dies) on a substrate (e.g. a silicon wafer). Transfer of the pattern is typically via imaging onto a layer of radiation-sensitive material (resist) provided on the substrate. In general, a single substrate will contain a network of adjacent target portions that are successively patterned. Known lithographic apparatus include so-called steppers, in which each target portion is irradiated by exposing an entire pattern onto the target portion at one time, and so-called scanners, in which each target portion is irradiated by scanning the pattern through a radiation beam in a given direction (the “scanning”-direction) while synchronously scanning the substrate parallel or anti-parallel to this direction. It is also possible to transfer the pattern from the patterning device to the substrate by imprinting the pattern onto the substrate.
There is an ongoing development in improving current lithographic apparatus. An aspect herewith is to increase the throughput (throughput is related to the number of substrates that can be processed in a certain time by a lithographic apparatus). For example, Dual Stage Lithographic apparatus generally have a larger throughput than Single stage apparatus since a substrate on a first substrate stage may be measured in a metrology station while another substrate on a second substrate stage is exposed in an exposure station on the basis of data measured previously in the metrology station. Another aspect is to improve the capability of lithographic apparatus to transfer patterns with smaller structures (but with a given quality) on substrates. For example, an Immersion lithographic apparatus is capable of transferring patterns with smaller structures in comparison with non-immersion lithographic apparatus (see for example EP 1486827, incorporated herein by reference).
In U.S. Pat. No. 5,969,441 (incorporated herein by reference) a Dual Stage lithographic apparatus is described that is provided with “H-drives” (see for example FIGS. 4, 5: respective X-actuators 105 and 107 connected to respective sets of opposite Y-actuators 109, 111 and 113, 115) for its substrate stages (substrate holders 11, 13). The described Dual Stage yields a relatively high throughput but a disadvantage is that the substrate stages need a “stage-swap” (according to the transition between FIG. 4 and FIG. 5 wherein substrate holder 11 is uncoupled from unit 25 and coupled to unit 27 and wherein substrate holder 13 is uncoupled from unit 27 and coupled to unit 25) for passing each other while moving between the metrology station and the exposure station (column 16, lines 47-52). The apparatus has the disadvantage that the stage-swap takes time, thus yielding a decreased throughput.
In U.S. Pat. No. 6,341,007 (incorporated herein by reference) (see in particular FIGS. 2, 3, 4) a Dual Stage lithographic apparatus is described that is provided with one exposure station situated between two metrology stations. The substrates in the batch are measured alternately in the metrology stations before exposure in the exposure station. The stages can not pass each other while moving between the metrology stations and the exposure station (see FIG. 3). A disadvantage of this lithographic apparatus is that it requires two metrology stations. Therefore, there is a necessity of providing a double substrate conveying path. The extra metrology station and the extra conveying path yield an expensive lithographic apparatus. Furthermore, the system layout takes relatively much (floor)-space in the facrories (large footprint). A further disadvantage is that this concept yields problems of a logistics nature. Furthermore, the lithographic apparatus is not suitable for immersion lithographic applications such that it is not capable to project relatively small structures on the substrates.